Three groups of 150 SPF chickens were spray-vaccinated with live Newca
stle disease La Sota-type vaccine (clone 30) at one day of age, and an
other three groups were NDV spray-vaccinated at 10 days of age. In eac
h of the two series of NDV-vaccinated groups, one group also received
at day-old 10(5) TCID50 of chicken anaemia virus (CAV) also and anothe
r group 10(5) TCID50 of CAV plus a low dose of virulent Marek's diseas
e virus (MDV). After one week, chickens of the groups which had been N
DV-vaccinated and CAV-infected at day-old, with or without MDV, showed
severe respiratory distress, conjunctivitis, drooping wings and ruffl
ed feathers. After two weeks, wet and inflamed eyes were observed. Aft
er three weeks the respiratory problems were overcome, but the entire
group showed retarded growth as compared with the group which had rece
ived NDV vaccine only. The 'respiratory sounds' were milder in the chi
ckens NDV-vaccinated at 10 days of age, about 10% of the chickens show
ing retarded growth. Mortality in CAV-infected chickens which had rece
ived NDV vaccine at day-old was above 30% at 4 weeks of age, and betwe
en 15 and 20% when NDV had been administered at the age of 10 days, an
d was 5% in the two NDC vaccine control groups. Decreased haematocrit
levels were measured in all four CAV-infected groups at 14 days of age
. In serum samples collected for 6 weeks at weekly intervals from chic
kens of the six groups, no differences were observed between HI antibo
dy titres against NDV virus. Thus, dual infection with CAV and live ND
V vaccine did not impair the humoral immune response against attenuate
d Newcastle disease vaccine.